1. Field of the Invention
The invention relates to the field of nanocavity optical arrays and in particular to an compact electrically and optically pumped multiwavelength nanocavity array in which each nanocavity is lithographically formed to define a corresponding predetermined spectral response of each nanocavity.
2. Description of the Prior Art
The past rapid emergence of optical micro cavity devices, such as vertical cavity surface emitting lasers (VCSELs) can be largely attributed to the high precision over the layer thickness control available during semiconductor crystal growth. High reflectivity mirrors can thus be grown with sub-nanometer accuracy to define high-Q cavities in the vertical dimension. Recently, it has also become possible to microfabricate high reflectivity mirrors by creating two- and three-dimensional periodic structures. These periodic xe2x80x9cphotonic crystalsxe2x80x9d can be designed to open up frequency bands within which the propagation of electromagnetic waves is forbidden irrespective of the propagation direction in space and to define photonic bandgaps. When combined with high index contrast slabs in which light can be efficiently guided, microfabricated two dimensional photonic bandgap mirrors provide us with the geometries needed to confine and concentrate light into extremely small volumes and to obtain very high field intensities. Here we propose to use these xe2x80x9cartificiallyxe2x80x9d microfabricated crystals in functional nonlinear optical devices, such as lasers, modulators, add/drop filters, polarizers and detectors.
A compact electrically and optically pumped multi-wavelength nanocavity laser, modulator and detector arrays uses lithography to define the precise spectral response of each element. High fields are applied within optical nanocavities to take advantage of photonic crystals filled with nonlinear materials. These nonlinearities and high fields are used to define tunable nanocavity lasers, detectors, routers, gates and spectrometers for wavelength and time division multiplexing applications.
Subwavelength nano-optic cavities can be used for efficient and flexible control over both emission wavelength and frequency. Similarly, nanofabricated optical waveguides can be used for efficient coupling of light between devices. This new capability allows the reduction of the size of optical components and leads to their integration in large numbers, much in the same way as electronic components have been integrated for improved functionality to form microchips. As high-Q optical and electronic cavity sizes approach a cubic half-wavelength, the spatial and spectral densities (both electronic and optical) increase to a point where the light-matter coupling becomes so strong that spontaneous emission is replaced by the coherent exchange of energy between the two systems.
The lithographic control over the wavelength and polarization supported within photonic crystal cavities is used to construct compact nanophotonic laser and detector arrays, as well as all-optical gates and routers. This spontaneous emission coupling efficiency can be even higher if the line width of the semiconductor emission is narrowed, as will be the case when using quantum dot active material. Therefore, single defect photonic crystal lasers represent in many ways the ultimate evolution of VCSELs, since control over both vertical and lateral spontaneous emission is possible. With most of the spontaneous emission funneled into a single optical mode, the photonic crystal laser can be modulated at much higher frequencies even close to threshold. The photonic crystal couples light emitted by one cavity, and uses it to optically pump another with negligible diffraction losses. Photonic crystals are also the perfect medium for constructing what have been termed xe2x80x9cphotonic moleculesxe2x80x9d, or interconnected cavities which can share and exchange photons. The emission wavelength of light from these photonic crystal lasers can be varied by simple adjustments of the lithographic pattern during their fabrication. Another unique feature of active photonic crystal cavities, which arises from their ability to limit the number of modes supported within the laser, is the ability to build high contrast modulators.
The invention is thus defined as a compact electrically and optically pumped multiwavelength nanocavity array comprising a plurality of nanocavities. Each nanocavity is defined in a photonic crystal where each nanocavity is lithographically formed to define a corresponding predetermined spectral response of each nanocavity. The plurality of nanocavities forming the array. The spectral response which is lithographically formed defines wavelength supported by the nanocavity. The spectral response which is lithographically formed may also define polarization supported by the nanocavity.
The array may be a laser array, detector array, all optical gate, all optical router, or a modulator. The photonic crystal is formed in one embodiment in active quantum well material.
In the illustrated embodiment the nanocavities are vertical cavity surface emitting lasers, VCSELs. The size of each of the nanocavities is approximately a cubic half-wavelength. In one embodiment at least one nanocavity laser is used as a pump for an adjacent nanocavity laser.
The array further comprises a nonlinear optical material filling the photonic crystal. The array may then be realized as a tunable nanocavity laser, detector, router, gate or spectrometer array. The array further comprises means for changing optical or electrical properties of the nonlinear optical material in each of the nanocavities, such as electrodes for applying a voltage or current across the array.
In one embodiment the photonic crystals in the array are defined in Sixe2x80x94Ge materials on silicon substrates disposed on insulators. The array may further comprise a silicon slab waveguide or integrated circuit integrated with the array.
In another embodiment the array further comprises a waveguiding layer disposed adjacent to the array. The waveguiding layer is substantially transparent to light from the array and is critically coupled to the nanocavities in the array.
While the apparatus and method has or will be described for the sake of grammatical fluidity with functional explanations, it is to be expressly understood that the claims, unless expressly formulated under 35 USC 112, are not to be construed as necessarily limited in any way by the construction of xe2x80x9cmeansxe2x80x9d or xe2x80x9cstepsxe2x80x9d limitations, but are to be accorded the full scope of the meaning and equivalents of the definition provided by the claims under the judicial doctrine of equivalents, and in the case where the claims are expressly formulated under 35 USC 112 are to be accorded full statutory equivalents under 35 USC 112. The invention can be better visualized by turning now to the following drawings wherein like elements are referenced by like numerals.